Method of activating cathodes



Jan. 13, 1948. H. A. POEHLER ETAL 2,434,517

' METHOD OF ACTIVATING CATHODES Filed lay 11, 1944 a r 1.9 F Mann-FM 1 1INVENTORS I V #fl-PGEI/(EE L Ff BEA/E. B

Y MM 1 ATTORNEY Pmnas Jan. 13, 1948 METHOD OF AQTIVATING CATHODES HorstA. Poehler, Long Island City,.N. Y., and Lester F. Keene, Montclair, N.J., assignors to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application May 11, 1944, Serial No.535,052

.6 Claims. (Cl. 316-4) This invention relates to a method of activat--cathodes, thermal activation of the cathode is al-' most exclusivelyused. However, sometimes due to such causes as lack of reducingmaterials in the core of the cathode, or conversely, to presence of alarge percentage of such elements as manganese, iron and the like beingexcessive, or, as

in the case of nickelate cathodes, to an oxidation of the reducingagent, thermal activation does not suflice. In such instances resort hasbeen made to activation by electrolysis of the' coating as one solutionof the problem, and to positive ion bombardment asanother solution.'However, the electrolytic method is excessively time consuming, oftenrequiring ten hours for accomplishment, and the positive-ion bombardmentmethod which has required introduction of an inert gas, has thedisadvantage of combating evil with evil and of being impractical inmany instances.

Manufacture of cathodes of the character indicated is generallyaccomplished by first coating a base member, secondly, converting theapplied coating and third, activating the converted coating. The basemember may be of such material as nickel, tungsten and the like. Coatingapplied thereto may be the carbonate of barium, strontium and the like.For brevity in description reference will be made to the base member asnickel and to the coating as applied as one containing barium. Thebarium carbonate is mixed with a binder and applied to the nickel.Conversion of the coating is performed with the oathode mounted in theelectronic device where it is to beused and is accomplished while thedevice is on the pumps for evacuation. By heating the cathode tosufilciently high temperature, the binder is driven off and thecarbonate converted to an oxide, which in the instance of the selectedexample, is barium oxide. The gases evolved, including the volatilizedbinder, are carried off on the exhaust. Thereafter, the oxide isactivated, usually after the device is sealed ofif. Activation is thestep of manufacture to condition the cathode surface to make it capableof copious emission. The more or less accepted theory of activation isthat the oxide at the surface is separated into its constituents whichin the selected instance results, in a film of barium on the cathodesurface and evolution of a small amount of oxygen, which of course, is agas. In due time the oxygen combines with some metal part in the deviceand being so .small in amount has never been considered or founddeleterious. In the present invention, the temporary presence of theoxygen is beneficial in that it promotes or supports ionization duringthe activating operation, but disappears before the device is put intoservice.

In its general aspects, the present invention has the objective ofimproving, simplifying and speeding cathode activation.

Another object-is to employ a novel method of ionization activation ofthe cathode.

Yet another object is to avoid need for specific introduction of gas forpurposes of ionization.

A further object is to provide an improved method of cathode activationwhich is performed while the electronic device is on the pump.

Other objects will appear to those skilled in the art to which theinvention appertains as the description progresses, both by directrecitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals ofreference indicate similar parts throughout the several views:

Figure 1 is a longitudinal sectional view of an exemplary electrondischarge device and associated instrumentalities for carrying out theinvention; and

Figure 2 is a cross-section of said device with indication of theelectron paths and magnetic field obtained by utilization of the presentinven tion.

In the specific embodiment of the invention illustrated in said drawing,the reference numeral l0 designates a cathode which is shown as of theindirectly heated type and accordingly hollow and having a heater lltherein. The specific device wherein the invention is illustrated is amagnetron having a cylindrical shell or body I2 within which anddirected toward the cathode are a plurality of anode segments i3separated by longitudinal splits or cavities I l.

Beyond the ends of the segments and within said body l2 are end spacesI5. The ends of the body I2 are sealed by plates or end caps l6. Leadsi! enter through the. side of body l2, ap-

propriately connecting with the heater and one connecting with thecathode, and both functioning to position and support the cathode withinthe center cavity l8 within the anode. The lead supporting and sealingmeans I! are of appropriate construction, one being shown as having anexhaust tubulation 2|, which is sealed, as usual, after the device isexhausted.

The cathode is one known in the trade as oxide coated, and whichgenerally comprises a nickel or other metal base having an externalcoating f a composition including such materials as barium, strontiumand the like, utilized, at least in part, in oxide form and reduced, atleast in part, by thermal or other activation. It is particularly withrespect to those cathodes which fail to produce adequate emission afterthermal activation that the present invention has its principal utility.The method accordingly includes, by preference, first applying thermalactivation in accordance with prior art practice, and thereafterapplying heating current to the heater and potential difference to thecathode and anode for obtaining electron emission from the cathode andelectron fiow toward the anode.

The invention in its specific embodiment is conducted by means ofpositive-ion bombardment, without introducing an inert gas. In itsbroadest aspect, the invention contemplates, for activation purposes,increasing the distance of travel of electrons to move in paths veryconsiderably greater than, and at least double the distance between thestraight-line distance between the cathode and anode. In consequence ofthis increased length of path during activation, the electrons have eacha greatly increased probability of collision with a gas atom, producingions by collision. In ionization by collision an electron impacting witha gas atom imparts to it sufiicient energy to remove one of theelectrons of the atom, leaving a positive ion, which in this case isattracted to the cathode and impinges upon it. The -ion has greatermass, and bombards the cathode more severely than an electron returningto the cathode. Due to action of the bombardment on the cathode, abeneficial activation of the cathode results.

For carrying out the invention, we introduce a magnetic field transverseto, or specifically at right angles to the normal electron path andelectric field, so as to make the electrons follow a curved, spiral, orcycloidal path from the cathode. By proper adjustment of the magneticfield, such path of the electron can be made quite long compared to itsnormal path without infiuence of a magnetic field. All electrons are notprecisely affected. Almost all reach the anode, although some do not, afew returning to the cathode, but all will travel in the region betweenthe cathode and anode with a marked increase of time and path interval,with correspondingly increased probability of ionization.

The magnetic field is appropriately established for the purpose, as byprovision of opposite permanent or electromagnetic poles 2|, 2| adjacentand immediately outside of the end plates of the magnetron shown. Themagnetic poles are accordingly coaxial with the cathode and set up themagnetic field longitudinally of the cathode or transverse to thedirection of normal electron fiow.

It is furthermore preferable to provide a magnetic field of materiallygreater strength next the anode than next the cathode, with the magneticfield next the cathode as near to zero as possible.

In realization of this desideratum, the magnetic field is preferablyestablished by a hollow core magnet which has the eflect of reducing thestrength of the magnetic field adjacent the oathode. The efiect of thereduced magnetic field adjacent the cathode is to prevent as much aspossible the return of electrons to the cathode. Upon entering thecomparatively magnetic fieldfree-space, an electron returning orinclining to return toward the cathode becomes subject to only oneforce, that of the electric field urging it back toward the anode.

In Figure 2, indication is given of the magnetic flux lines in crosssection by the dots in the outer portion of the central cavity, whereasat the inner portion of the central cavity, such flux lines do notappear in such great number due to the shape of the pole pieces.Likewise in said Figure 2, indication has been given by dotted lines 23of the gyrating path of several electrons indicative of the influence onthe electrons of the magnetic field and the resultant increase in lengthof such path over the normal straight-line radial path from cathode toanode. It is by virtue of this material increase of path of theelectrons which affords greater opportunity for collision of electronswith gas atoms and releasing ions therefrom, charging the ions andcausing the ions to bombard the cathode.

We claim: I

1. The hereindescribed method of cathode activation, which comprisesemitting electrons from the cathode and simultaneously subjecting regionaround the cathode to a magnetic field and with said field havinggreatest intensity remote from the cathode for increasing the electronpath.

2. The hereindescribed method of cathode activation comprising emittingelectrons from said cathode, producing ions therewith in a magneticfield having greatest intensity remote from the cathode, and bombardingthe cathode by said ions.

3. The hereindescribed method of cathode activation comprising thermallyactivating the cathode, emitting electrons from the thermally activatedcathode, spiraling said electrons through a plurality of convolutionsremote from the cathode, producing ions therewith, and furtheractivating said cathode by bombardment from said ions.

4. The hereindescribed method of cathode activation of a cathode mountedin an anode cavity, comprising emitting electrons from said cathodetoward the anode, applying a magnetic field in the region between saidcathode and anode and increasing the electron path substantially morethan electron path of normal operation, producing ionsin said magneticfield with said electrons, and bombardingthe cathode by said ions.

5. The hereindescribed method of cathode activation of a cathode mountedin an anode cavity, comprising emitting electrons from said cathodetoward the anode, applying a magnetic field in the region between saidcathode and anode, of greater intensity next the anode and lesserintensity next the cathode, producing ions in said magnetic field withsaid electrons, and bombardingthe cathode by said ions. 1

6. The hereindescribed method of cathode activation of a cathode mountedin a cavity of an anode, comprising thermally activating the oathode,emitting electrons from the thermally activated cathode toward theanode, applying a mag netic field to said cavity transverse to thenormal direction of fiow or said electrons from cathode to anode andwith greater intensity next the anode than next the cathode, therebycausing the electrons to follow a curved path in a region remote fromthe cathode and promoting ionization, and bombarding the cathode withtons of said ionization.

HOB-E51 A. POE. LESTER, F.

. REFERENCES CITED The following references are of. record in the fileof this patent:

' a a lsTATEB RAE Number Name Date 2,115,52E mm et al. New. Am. 26. 1938Number Nmmbet" ammo

